I'm not sure if that is a global problem, but I tried it a few times and every time it did it like that.
Problem 4500.
When I click on bA18 (the first correct move) and get wB19 in response, there are two incorrect moves marked: B13 and A13 (I know because I looked at navigation afterwards).
Usually, when I hover mouse arrow over an intersection, a transparent stone appears to show how the stone would be placed if I clicked there.
Now, after my first move, when I'm choosing the second one, I get the transparent stone in every empty intersection where I hover the mouse arrow, except when I hover it over either of the two wrong-marked intersections.
If this pattern works generally, then it is a great cheat, I think. I also wouldn't like to refrain from the hovering, because I like to see that transparent stone, it somehow helps to think (for a beginner anyway).
Thanks!
{Posted by eyedam}